(1) Field of the Invention
The present invention relates to a bulkable yarn for weaving or knitting into fabrics which are really natural silk-like in general appearance, luster, hand liveliness and hue, and a process and an apparatus for the preparation of the same.
The term "bulkable filamentary yarn", as used herein, comprehends a thermoplastic multi-filamentary yarn having mixed differential boil-off shrinkage portions at considerably short intervals along the yarn length, said portions being composed of the filaments differing in shrinkage among the filaments as well as within each of the filaments, and developes its latent bulkiness to show silk-like hand and fullness when heat-relaxed. Although the word "fullness" means bulky state in general it is characteristic of silk, and distinguished, for example, from a bulky state of crimped yarn.
(2) Description of the Prior Art
As disclosed in the specification of British Pat. No. 1,510,337 or Japanese Patent Publication No. 47550/1972 and No. 18535/1976, it is well known to produce a textured yarn with crimps and length-difference induced among the constituent filaments by contacting a thermoplastic filamentary yarn instantaneously to a heated body (roll) of dry heat type under a tension below the thermal shrinkage stress of the yarn (more concretely under substantially tension free state) wherein a part of the constituent filaments shrinks intermittently and, accordingly, an another part of the same is made puckered to form loops and slack protrusions.
Thus obtained textured yarn bears on its surface a large number of loops and the like, and as the result, although the yarn presents silk-like hand and tactility to some extent, it has left many problems unsolved in view of a commercial production as follows:
(i) Since the filamentary yarn undergoes an irregular thermal treatment in transverse and lengthwise direction, splashed pattern streaks arise on the surface of a woven or knitted fabric made up of such yarn. This is due to an unstable heat-treating process because the filamentary yarn is subjected to contact heat-treatment in a state substantially free from tensioning which state, in turn, prevents smooth running of the yarn over the heated body.
In order to avoid such streaks, one can imagine in his mind that the partial, predetermined filaments shall undergo the heat-treatment selectively at a constant ratio. But, the limitation of "instantaneous" with regard to a treatment time makes it impossible, for example, to heat always one-half of all the filaments and actually makes a constant variance of the numbers of the filaments to be heated. Further a processing speed of the above method becomes limitative of its own accord.
(ii) As the result of shrinking filamentary groups partially, loops and the like are formed on the surface of the yarn. The existence of such protrusions deteriorates the handling and running property of the yarn, and accordingly, the weaving or knitting efficiency (performance) especially. In addition, the surface appearance of fabrics obtained is spoiled its commercial value.
For this reason, such process has also been proposed to re-heat the loop yarn above mentioned to diminish said loops in order to improve the handling and running property. In this process, however, the difference of boil-off shrinkage between the more shrinkable portions and the less, shrinkable portions originally induced in the form of the loop yarn is easily reduced to a quite limited range.
Therefore, such hand and tactility originally possessed by the loop yarn can never be expected to develope again.
(iii) Since the textured (loop) yarn is composed of partially shrunken filaments under an extremely lower tension, it possesses flow portions scattered therein. Due to the existence of these portions, the yarn is stretched with irregularity during weaving or knitting operations so that tight spots arise inevitably and fabrics obtained tend not to be restored to the original state after it is deformed.
(iv) Although the textured yarn possesses both the more shrinkable components and the less shrinkable components, these components exist in separate state (not commingled state), which state is mainly attributed to the reason that the process itself adopts anyway one-side heating of the starting yarn under an instantaneous period of time. Accordingly, the loop or textured yarn obtained, when heat-relaxed, for example, at a dyeing stage, only exhibits a puckered form as a whole and therefore, silk-like effects in the term of "moderate fullness" as realized by the mixed, differential shrinkage characteristics is lowered.
As mentioned above, conventional silk-like yarn of thermoplastic material with the differential shrinkage characteristics induced therein has always offered serious problems such as dyeing speck, lower restoring power and deterioration of weaving efficiency, and even at present silk-like aesthetics inherently possessed by such yarns have not been manifested sufficiently in fabrics.